Silver halide-using photography is superior in photographic characteristics, e.g., photographic speed, facility of gradient control, etc., to other photographic techniques, such as electrophotography, diazo photography, and so on. Therefore, it has so far been employed most prevailingly. In recent years, techniques have been developed which enable simple and rapid formation of images by changing the image-forming processing in the silver halide-using photography from the conventional wet process using a developing solution or the like to a dry process using a heat-applying means or the like.
Heat-developable photosensitive materials are well-known in the photographic art, and such materials and the processes therefor are described, e.g., in Shashin Kogaku no Kiso (Fundamentals of Photographic Engineering), pp. 553-555, Corona Co. (1979); Eizo Joho (Information on Images), p. 40 (April 1978); Neblette's Handbook of Photography and Reprography, 7th Ed., pp. 32-33, Van Nostrand Reinhold Company; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777; and Research Disclosure, RD No. 17029, pp. 9-15 (June 1978).
Many methods for obtaining color images have been proposed. For instance, as for the method of forming color images by binding couplers to oxidation products of developing agents, there are proposed the combinations of p-phenylenediamine type reducing agents with phenolic or active methylene-containing couplers in U.S. Pat. No. 3,531,286, the reducing agents of p-aminophenol type in U.S. Pat. No. 3,761,270, the reducing agents of sulfonamidophenol type in Belgian Pat. No. 802,519 and Research Disclosure, Vol. 137, pp. 31-32 (Sept. 1975), and the combinations of sulfonamidophenol type reducing agents with 4-equivalent couplers in U.S. Pat. No. 4,021,240.
In addition, as for the method of forming positive color images using the light-sensitive silver dye bleach process, useful dyes and bleaching methods are described in, e.g., Research Disclosure, RD No. 14433, pp. 30-32 (April 1976), ibid., RD No. 15227, pp. 14-15 (Dec. 1976), and U.S. Pat. No. 4,235,957.
Moreover, the method of forming images by heat development, in which compounds having a dye moiety in advance and capable of releasing a mobile dye under a high temperature condition in correspondence or counter-correspondence to the reaction of reducing silver halide to silver are utilized, is disclosed in published unexamined European Patent Application Nos. 76,492 and 79,056, and Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
These heat-developable photosensitive materials are characterized by the development-processing to which they are to be subjected. The development-processing is carried out under heating in a condition that water is substantially absent from the developing system. Such dry processing has a great advantage in that it can provide images simply and rapidly.
On the other hand, the heat-developable photosensitive materials necessitate therein the prior incorporation of all photographic agents necessary to effect development because they cannot expect a supply of desired photographic agents from a developing solution or the like. However, if a photographic agent is added to a photosensitive material in an active form, it tends to undergo reactions with other components present in the photosensitive material or decomposes under the influence of heat or oxygen during storage prior to processing. Therefore, it becomes impossible to fully achieve the expected capabilities at the time of processing.
One solution to this problem is a method in which a photographic agent is converted into a substantially inactive form by blocking the active group, that is, a precursor thereof, and then, the precursor is added to a photosensitive material.
When the useful photographic agent is a dye, a functional group having a great effect on spectral absorption of the dye is blocked and thereby, its spectral absorption is shifted to the shorter or the longer wavelength side. Under this circumstance, even if the blocked dye is also present in a silver halide emulsion layer with a spectral sensitivity in the wavelength region corresponding to the spectral absorption of the original dye, a lowering of sensitivity due to the so-called filter effect does not occur. Therefore, it can be used advantageously.
When the photographically useful agent is an anti-foggant or a development inhibitor, blocking of the active group can offer many advantages, e.g., desensitization due to adsorption onto light-sensitive silver halide grains and formation of silver salts upon storage can be inhibited, and at the same time, through timely release of such photographic agents, fog can be reduced without impairing photographic speed, fog arising from over development can be depressed, development can be stopped at a desired time, and so on. When the photographically useful agent is a developer, assistant developer, or a fogging agent, blocking the active group or the adsorptive group can offer the advantages that various photographically adverse effects due to conversion of the developer into semiquinones or oxidants through air oxidation upon storage can be prevented, and/or injection of electrons into silver halide can be prevented from occurring during storage. Thereby, generation of fog nuclei can be inhibited. This results in the realization of stable processing and the like. Where the photographically useful agent is a bleach accelerator or a bleach-fix accelerator, blocking the active group can offer the advantages that in storing the sensitive material, reactions with other components also present with such an agent can be suppressed, while in processing it, the expected ability can be brought into full play upon removal of the blocking group at the time needed.
Several techniques for blocking photographic agents which are usable in conventional photographic materials are already known. For example, well-known techniques involve utilization of a blocking group such as an acyl group, a sulfonyl group or the like, as described in Japanese Patent Publication No. 44805/72, utilization of a blocking group which releases a photographic agent due to the so-called reverse Michel's reaction, as described in Japanese Patent Publication Nos. 17369/79, 9696/80, and 34927/80, utilization of a blocking group which releases a photographic agent by an intramolecular electron transfer accompanying the production of quinonemethide or analogues thereof, as described in Japanese Patent Publication No. 39727/79 and Japanese Patent Application (OPI) Nos. 135944/82, 135945/82, and 136640/82, utilization of the intramolecular ring-closure reaction described in Japanese Patent Application (OPI) No. 53330/80, utilization of the cleavage of a 5- or 6-membered ring described in Japanese Patent Application (OPI) Nos. 76541/82, 135949/82, and 179842/82, and so on. However, all of these known techniques utilize hydrolysis or dehydrogenation due to attack of OH.sup..crclbar. at the time of wet development, and no precursor techniques applicable to dry processing in which organic bases are used has been known.